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Energy vs force vs work vs power

  1. Aug 30, 2014 #1
    In physics, I know that all of these terms are used. I need to brush up on my physics and I plan to study during my free time (I want to master the conversion from one form of energy into another, example; electrical to mechanical & vice versa)

    So as a generalization, what is the difference between the four? I know that magnetism is a force, electrical field involves force and energy, watts is energy and force as well (where volts is force and amps is energy; energy = force times dx I think) and so fourth. You don't have to go to in depth, just helping me distinctively knowing how to define all four and their different application in physics is enough for me (In high school, these terms which seem synonymous in physics class were never clarified from the beginning to the end, and I didn't realize the importance until now) Right now I just want to create a stepping stone for future success or to at least have a fighting chance for success. :)

    *Another example
    Technically, you can't convert Joules to horsepower, since they are units of different measurements. Joules is a unit of work or energy, while horsepower is a unit of power, i.e. the time derivative of work. There must be a time interval specified somewhere. But Joules don't equal watts either--one's a measurement of energy, one's a mesurement of power. 1 Watt = 1 Joule / 1 sec. But you can convert watts into horsepower which would be;
    1 horsepower = 745.699872 Watts
    Last edited: Aug 30, 2014
  2. jcsd
  3. Aug 30, 2014 #2


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    Why don't you look up the actual definitions instead of guessing what they are (hint: you got all of them wrong)? That's the best way to start into any question. Then you can ask more specific and informed questions.
  4. Aug 30, 2014 #3
    Hello russ_watters,

    I think that is my problem because I looked up all of the definitions online and that is what I came up with, your response would be a bit more helpful if you sited a link or tutorials where I may look up the correct definitions to these terms.
  5. Aug 30, 2014 #4


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    I think the best way to start, would be to learn the basic units of each:

    Right off, you see that "energy" and "work" are somehow related, as they have the same unit of measurement. But then you will ask; "Why don't they just call it ewonerrkgy, since they are the same"? At which point, we would tell you; "Because they are not the same".

    A 1 kg rock sitting on a shelf, 1 meter off the floor, has a potential energy, of 9.8 joules.

    But no work is being done by the rock when it sits there. So energy and work, are not the same.

    And then, we will tell you, that it only gets worse from there.
  6. Aug 31, 2014 #5


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    Seems like an unthinkable idea to a lot of our new posters. I seem to have been seeing an inordinate number of newbie posts recently that clearly show zero attempt at doing any research.
  7. Aug 31, 2014 #6
    So I could now better compare all of them especially work and energy, since work is kinetic energy. And now I see that a Joule is strictly a measurement of mechanical work/mechanical energy. Since magnetism is a force, is a magnet therefore a potential force or would that more apply to an electromagnet? I could see how when these overlap that some problems may emerge(confusion) such as magnetism is a force, but when a permanent magnet or an energized object is moved back and fourth an electrical field is generated and I'm guessing that Faraday's Law or Gauss Law would summarize this relationship between force (with virtual photons and photons [magnetic and electrical fields])*1, and energy (electrical energy that is generated by induction)*2

    *1. at the bottom from this post "Relationship between electricity and magnetism"

    *2. this post talks about the relationship between magnetic and electrical fields "Relationship electricity and magnetism"

    I understand that pressure is like force but it deals with fluids, but as for field, this term relies on force as defined by wikipedia

    "field, In physics, a region in which each point is affected by a force. Objects fall to the ground because they are affected by the force of earth's gravitational field (see gravitation)."

    but a field differs from a wave where a wave in this sense deals with energy as stated again by wikipedia

    "In physics, a wave is disturbance or oscillation that travels through matter or space, accompanied by a transfer of energy. Wave motion transfers energy from one point to another, often with no permanent displacement of the particles of the medium—that is, with little or no associated mass transport."

    I really appreciate your guys' help, and again I am thankful because you guys helped me clear up some basics. I apologize because lately my head has been a blunder because I am not taking much science courses this semester and I'm caught in the middle of doing some projects where I finally have the opportunity to exercise this beautiful field of study!

    As for phinds, I know you mean well but in my case I covered a lot of grounds in physics in high school. But unfortunately the professor did not explain during his lecture many of these simple things that I posted which made me more confused later on down the road. I could easily find the formula for each but I guess I need an explanation to go along with how they are all similar and how they all differ, I am not yet up there in physics but I plan to get there soon. I guess I just wanted an explanation in which I can understand and better compare all of these terms instead of reading them in the order of a textbook (because the textbooks of today don't seem to order things based on relevancy but rather switch chapters around to sell "new" editions) in which the information doesn't stick too well with me and leaves me more questions (I don't catch their relevancy until later on, because I'm the kind of learner that has to build on prior knowledge or else I might get lost)
    Last edited: Aug 31, 2014
  8. Aug 31, 2014 #7


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    Understandable. It's helpful when someone can help boil everything down to the basic points and not get lost in all the details and analogies and such.
  9. Aug 31, 2014 #8


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    Read first: http://hyperphysics.phy-astr.gsu.edu/hbase/work.html and watch this: .

    Not knowing the definitions, your statements have no sense.
    Work is not kinetic energy. Magnetism is a phenomenon, not a force. Pressure is not field, and it is not force, either...

    Last edited by a moderator: Sep 25, 2014
  10. Aug 31, 2014 #9


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    If you weren't impressed with your teacher then why not get it all out of a book? You asked about four simple formulae. Look up any elementary text about Physics and it will be presented in, at least, an alternative way. You have, at your fingertips, thousands of sources of this sort of information and you will be far better doing your own hunting and research than expecting PF to help you at the very start. You will get a much better response (positive + helpful + indulgent) once you have shown that you can make an effort. We do not jump on people as a matter of course. :smile:
  11. Aug 31, 2014 #10


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    Have you tried putting the title of your thread into google? Many useful hits.
  12. Aug 31, 2014 #11
    I like to think of it this way

    FORCE = how much strength you have..
    if someone asks you "can you lift a 50kg object off the floor?", you think about "how much force i need to exert, or do i have enough strength in me to lift it" .. if you don't have the required strength to put the sufficient force, (in this case about 500N) you can't lift it

    WORK = how much.. well work u can do :D
    If you lift that 50kg object by 1m, then u do 500J of work ..if u lift it by 10m, you do 5000 J of work.

    ENERGY = something that allows u to do the work .. capacity to do the work..
    to do work u need energy.. both have same units.

    now.. imagine.. i ask u to lift that 50kg object, 10m high.. can you do it? ..
    a)You need to put atleast 500N of force (so thats the strength consideration)
    b) You need to do 5000J of work, hence u need to have atleast 5000J of energy

    you may have the required energy do to do the work, but you may not have the required strength .. (what a shame that would be)

    this example immediately tells u how different force and energy are..

    Lastly.. imagine you and I lift this 50 kg object by 1m. You do it in 2 seconds, i do it in 5 seconds.
    who did more work? (well its the same right? both did 500 J of work.. and we both spent 500 J of energy in doing so)

    but.. You did the work quicker than I did. In todays world, speed matters, how fast you can get the job done matters a lot. if we were both labourers, then people would prefer you over me (although we both have the required energy) . This concept of how fast you can do work is what we called as POWER.

    That guys is powerful .. (he can do work very fast)
    That guy is energetic .. (he can do a lot of work and thus have a lot of energy inside him)
    That guy is very strong.. (he can put a lot of force )

    This is usually the way I like to think about these terms
  13. Aug 31, 2014 #12


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    Everyone at PF means well. But I have to agree with Russ, ehild, phinds, and my original thoughts. Your OP and subsequent post look like you took a bag of dice, wrote physics words on each side, threw out the dice, and made sentences up, based on their order.

    It's pure nonsense.

    Your "prior knowledge" appears to be close to zero, based on my aforementioned "dice throwing" model of physics.

    And jumping into:
    will of course make no sense to you.

    You don't even know what a "Joule" is.

    How can you build a house of physics, if you have no foundation?

    And physics isn't just a house, it's a freakin' palace.

    Palaces take time to build.

    Grok the "Joule", young Shoe-She-Boy, and then come back, and post a coherent question.



    as always: ok2di&b
  14. Aug 31, 2014 #13


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    Sorry if you don't like our methods, but you will learn better if you go slower, work more coherently, and put more meaningful effort into it.

    Try this: Google each of the terms and write down the verbal and mathematical definitions of each. With them sitting right next to each other, the relationships become clearer.
    Last edited: Sep 2, 2014
  15. Sep 1, 2014 #14


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    Perhaps not perfect but..

    Energy - The ability or potential to do work.
    Work - The transfer or conversion of energy from one form to another
    Power - The rate at which work is done.
  16. Sep 2, 2014 #15


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    You forgot "Force", and maheshshenoy's "Strength":

    Just pulled my ©1986 edition of Halliday & Resnick's, college text, titled; "FUNDAMENTALS OF PHYSICS", and did not see an index reference to "Strength".

    ps. I'm not 100% sure, but apparently "caps lock", when titling books back in the '80's, was not considered shouting.


  17. Sep 2, 2014 #16


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    Wikipedia defines Force as "any influence which tends to change the motion of an object"..


    Strength is tricky as I don't think there is one single definition. Perhaps look at Ultimate Tensile strength for which the unit is the Pascal. In effect the force per unit area required to break something.
  18. Sep 2, 2014 #17


    Staff: Mentor

    I would stay away from magnetism and electricity until you understand these quantities in terms of mechanical quantities first. Luckily, they are simple to understand in mechanics:

    Work is force times distance. (no movement = no work, same force bigger distance = more work, etc.)
    Power is work divided by time. (same work done in a shorter time = higher power)
    Energy is the capacity to do work. (an object with kinetic energy can do work by colliding with something)
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